The present invention relates to an overshoot control technology at turning ON the power supply of a constant voltage generating circuit, and for example, the present invention relates to a technology which can be effectively adapted to a microcomputer or the like in which a step-down voltage generating circuit for generating an internal voltage is loaded.
As a technology for controlling overshoot in a constant voltage generating circuit when the power supply voltage thereof is turned ON, a clamping transistor is provided to realize clamping, by making an output terminal of an output buffer conductive to the ground voltage only for the predetermined period when the power supply is turned ON, to a constant voltage circuit, for example, comprising a differential amplifying circuit to receive the standard voltage as the reference potential and an output buffer (output stage circuit) which is connected, through negative feedback, to the differential amplifying circuit for conducting the current output operation. Overshoot of the relevant output terminal which is generated when the power supply is turned ON can be controlled using such clamping transistor (FIG. 1 in the Patent Document 1). In addition, the overshoot can be controlled through quick defining of the operating condition by improving operation rate of the differential amplifying circuit when the power supply is turned ON (FIG. 2 in the Patent Document 1) and through cut-off of a current supplying transistor circuit of the output buffer (FIG. 5 in the Patent Document 1). The Patent Document 2 can also be listed additionally as the technology for preventing overshoot by providing a clamping transistor to an output of the output buffer of a low voltage generating circuit.
[Patent Document 1]
Japanese Unexamined Patent Publication No. Hei 10(1998)-214121.
[Patent Document 2]
Japanese Unexamined Patent Publication No. 2001-358575 (FIG. 2).